Wireless Power Systems With Interference Mitigation

ABSTRACT

A wireless power system has a wireless power transmitting device and a wireless power receiving device. A clock signal may be provided to inverter circuitry in wireless power transmitting circuitry at a power transmission frequency. The clock signal may cause transistors in the inverter circuitry to turn on and off to create AC current signals through the wireless power transmitting coil. The clock signal may be processed to mitigate electromagnetic interference in the system.

This application claims the benefit of provisional patent applicationNo. 63/233,528, filed Aug. 16, 2021, which is hereby incorporated byreference herein in its entirety.

FIELD

This relates generally to power systems, and, more particularly, towireless power systems for charging electronic devices.

BACKGROUND

In a wireless charging system, a wireless power transmitting devicetransmits wireless power to a wireless power receiving device. Thewireless power transmitting device uses a wireless power transmittingcoil to transmit wireless power signals to the wireless power receivingdevice. The wireless power receiving device has a coil and rectifiercircuitry. The coil of the wireless power receiving device receivesalternating-current wireless power signals from the wireless powertransmitting device. The rectifier circuitry converts the receivedsignals into direct-current power.

SUMMARY

A wireless power system has a wireless power transmitting device and awireless power receiving device. The wireless power transmitting devicemay include a coil and wireless power transmitting circuitry coupled tothe coil. The wireless power transmitting circuitry may be configured totransmit wireless power signals with the coil. The wireless powerreceiving device may include a coil that is configured to receivewireless power signals from the wireless power transmitting device andrectifier circuitry that is configured to convert the wireless powersignals to direct current power.

A clock signal may be provided to inverter circuitry in the wirelesspower transmitting circuitry at a power transmission frequency. Theclock signal may cause transistors in the inverter circuitry to turn onand off to create AC current signals through the wireless powertransmitting coil (also at the power transmission frequency). Tomitigate electromagnetic interference (EMI) in the system, the clocksignal used to control the inverter may be frequency dithered. Thiseffectively dithers the power transmission frequency of the wirelesspower transfer between the wireless power transmitting device and thewireless power receiving device.

The wireless power transmitting device may include dithering circuitryand clock modulating circuitry that are used to implement a spreadspectrum clocking technique (sometimes referred to as clock dithering).In spread spectrum clocking, the edge of the clock waveform isintentionally modified such that the signal's spectrum is spread aroundthe target frequency for the clock signal. This reduces the EMIassociated with the target frequency of the clock signal.

The dithering circuitry in the wireless power transmitting device maygenerate an optimal modulating waveform for the clock signal based onthe real time operating conditions in the wireless power system. Thedithering circuitry may take into account information such as wirelesspower receiving device state of charge information, a maximum frequencyjitter constraint, an occupied bandwidth constraint, wireless powerreceiving device parameters, wireless power transmitting deviceparameters, and/or a clock waveform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative wireless power systemin accordance with an embodiment.

FIG. 2 is a circuit diagram of an illustrative wireless power system inaccordance with an embodiment.

FIG. 3 is a schematic diagram of an illustrative power transmittingdevice that includes dithering circuitry in accordance with anembodiment.

FIG. 4 is a graph of power as a function of frequency for a powertransmitting device in accordance with an embodiment.

FIG. 5 is a graph of an illustrative modulating waveform that may beused to modulate a clock signal in a power transmitting device inaccordance with an embodiment.

FIG. 6A is a graph of an illustrative modulating waveform that has aregular step shape in accordance with an embodiment.

FIG. 6B is a graph of an illustrative modulating waveform that has anirregular step shape in accordance with an embodiment.

FIG. 7 is a schematic diagram of an illustrative system for testing theperformance of different modulating waveforms in accordance with anembodiment.

FIG. 8 is a schematic diagram of an illustrative system that is used toobtain data for correlating power transmitter device parameters to apower receiving device state of charge magnitude in accordance with anembodiment.

FIG. 9 is a schematic diagram of illustrative dithering circuitry in apower transmitting device that is used to output an optimized modulatingwaveform for frequency dithering in accordance with an embodiment.

FIG. 10 is a flowchart of illustrative operations for operating a powertransmitting device that performs frequency dithering of a clock signalin accordance with an embodiment.

FIG. 11 is a diagram showing an illustrative frequency-shift keying(FSK) modulation bit encoding scheme in accordance with someembodiments.

DETAILED DESCRIPTION

A wireless power system includes a wireless power transmitting device.The wireless power transmitting device wirelessly transmits power to awireless power receiving device. The wireless power transmitting devicemay be a charging puck, a charging mat, a portable electronic devicewith power transmitting capabilities, a removable battery case withpower transmitting capabilities, or other power transmitter. Thewireless power receiving device may be a device such as a cellulartelephone, tablet computer, laptop computer, removable battery case,electronic device accessory, wearable such as a wrist watch, or otherelectronic equipment. The wireless power receiving device uses powerfrom the wireless power transmitting device for powering the receivingdevice and for charging an internal battery.

Wireless power is transmitted from the wireless power transmittingdevice to the wireless power receiving device by using an inverter inthe wireless power transmitting device to drive current through one ormore wireless power transmitting coils. The wireless power receivingdevice has one or more wireless power receiving coils coupled torectifier circuitry that converts received wireless power signals intodirect-current power.

An illustrative wireless power system (wireless charging system) isshown in FIG. 1 . As shown in FIG. 1 , wireless power system 8 includesa wireless power transmitting device such as wireless power transmittingdevice 12 and includes a wireless power receiving device such aswireless power receiving device 24. Wireless power transmitting device12 includes control circuitry 16. Wireless power receiving device 24includes control circuitry 30. Control circuitry in system 8 such ascontrol circuitry 16 and control circuitry 30 is used in controlling theoperation of system 8. This control circuitry may include processingcircuitry associated with microprocessors, power management units,baseband processors, digital signal processors, microcontrollers, and/orapplication-specific integrated circuits with processing circuits. Theprocessing circuitry implements desired control and communicationsfeatures in devices 12 and 24. For example, the processing circuitry maybe used in processing user input, handling negotiations between devices12 and 24, sending and receiving in-band and out-of-band data, makingmeasurements, estimating power losses, determining power transmissionlevels, and otherwise controlling the operation of system 8.

Control circuitry in system 8 may be configured to perform operations insystem 8 using hardware (e.g., dedicated hardware or circuitry),firmware and/or software. Software code for performing operations insystem 8 and other data is stored on non-transitory computer readablestorage media (e.g., tangible computer readable storage media) incontrol circuitry 8. The software code may sometimes be referred to assoftware, data, program instructions, instructions, or code. Thenon-transitory computer readable storage media may include non-volatilememory such as non-volatile random-access memory (NVRAM), one or morehard drives (e.g., magnetic drives or solid state drives), one or moreremovable flash drives or other removable media, or the like. Softwarestored on the non-transitory computer readable storage media may beexecuted on the processing circuitry of control circuitry 16 and/or 30.The processing circuitry may include application-specific integratedcircuits with processing circuitry, one or more microprocessors, acentral processing unit (CPU) or other processing circuitry.

Power transmitting device 12 may be a stand-alone power adapter (e.g., awireless charging mat or charging puck that includes power adaptercircuitry), may be a wireless charging mat or puck that is coupled to apower adapter or other equipment by a cable, may be a portable device,may be equipment that has been incorporated into furniture, a vehicle,or other system, may be a removable battery case, or may be otherwireless power transfer equipment.

Power receiving device 24 may be a portable electronic device such as acellular telephone, a laptop computer, a tablet computer, a wearablesuch as an earbud or wrist watch, a wirelessly charged removable batterycase for an electronic device, or other electronic equipment. Powertransmitting device 12 may be coupled to a wall outlet (e.g., analternating-current power source), may have a battery for supplyingpower, and/or may have another source of power. Power transmittingdevice 12 may have an alternating-current (AC) to direct-current (DC)power converter such as AC-DC power converter 14 for converting AC powerfrom a wall outlet or other power source into DC power. DC power may beused to power control circuitry 16. During operation, a controller incontrol circuitry 16 uses power transmitting circuitry 52 to transmitwireless power to power receiving circuitry 54 of device 24. Powertransmitting circuitry 52 may have switching circuitry (e.g., invertercircuitry 61 formed from transistors) that is turned on and off based oncontrol signals provided by control circuitry 16 to create AC currentsignals through one or more wireless power transmitting coils such aswireless power transmitting coil(s) 36. These coil drive signals causecoil(s) 36 to transmit wireless power. Multiple coils 36 may be arrangedin a planar coil array (e.g., in configurations in which device 12 is awireless charging mat) or may be arranged to form a cluster of coils(e.g., in configurations in which device 12 is a wireless chargingpuck). In some arrangements, device 12 (e.g., a charging mat, puck,portable electronic device such as a cellular telephone, etc.) may haveonly a single coil. In other arrangements, a wireless charging devicemay have multiple coils (e.g., two or more coils, 2-4 coils, 5-10 coils,at least 10 coils, fewer than 25 coils, or other suitable number ofcoils).

As the AC currents pass through one or more coils 36,alternating-current electromagnetic (e.g., magnetic) fields (wirelesspower signals 44) are produced that are received by one or morecorresponding receiver coils such as coil(s) 48 in power receivingdevice 24. Device 24 may have a single coil 48, at least two coils 48,at least three coils 48, at least four coils 48, or other suitablenumber of coils 48. When the alternating-current electromagnetic fieldsare received by coil(s) 48, corresponding alternating-current currentsare induced in coil(s) 48. The AC signals that are used in transmittingwireless power may have any suitable frequency (e.g., 100-400 kHz,etc.). Rectifier circuitry such as rectifier circuitry 50, whichcontains rectifying components such as synchronous rectificationmetal-oxide-semiconductor transistors arranged in a bridge network,converts received AC signals (received alternating-current signalsassociated with electromagnetic signals 44) from one or more coils 48into DC voltage signals for powering device 24.

The DC voltage produced by rectifier circuitry 50 (sometime referred toas rectifier output voltage Vrect) can be used in charging a batterysuch as battery 58 and can be used in powering other components indevice 24. For example, device 24 may include input-output devices 56.Input-output devices 56 may include input devices for gathering userinput and/or making environmental measurements and may include outputdevices for providing a user with output. As an example, input-outputdevices 56 may include a display, speaker, camera, touch sensor, ambientlight sensor, and other devices for gathering user input, making sensormeasurements, and/or providing user with output. Device 12 may includeinput-output devices 69 (e.g., any of the input-output devices describedin connection with input-output devices 56).

Device 12 and/or device 24 may communicate wirelessly using in-band orout-of-band communications. Device 12 may, for example, have wirelesstransceiver circuitry 40 that wirelessly transmits out-of-band signalsto device 24 using an antenna. Wireless transceiver circuitry 40 may beused to wirelessly receive out-of-band signals from device 24 using theantenna. Device 24 may have wireless transceiver circuitry 46 thattransmits out-of-band signals to device 12. Receiver circuitry inwireless transceiver 46 may use an antenna to receive out-of-bandsignals from device 12. In-band transmissions between devices 12 and 24may be performed using coils 36 and 48. With one illustrativeconfiguration, frequency-shift keying (FSK) is used to convey in-banddata from device 12 to device 24 and amplitude-shift keying (ASK) isused to convey in-band data from device 24 to device 12. Power may beconveyed wirelessly from device 12 to device 24 during these FSK and ASKtransmissions.

Control circuitry 16 has measurement circuitry 41. Measurement circuitry41 may include voltage measurement circuitry (e.g., for measuring one ormore voltages in device 12 such as a coil voltage associated with awireless power transmitting coil) and/or current measurement circuitry(e.g., for measuring on or more currents such as a wireless powertransmitting coil current).

Control circuitry 30 has measurement circuitry 43. Measurement circuitry43 may include voltage measurement circuitry (e.g., for measuring one ormore voltages in device 24 such as a coil voltage associated with awireless power transmitting coil and/or a rectifier output voltage)and/or current measurement circuitry (e.g., for measuring on or morecurrents such as wireless power receiving coil current and/or rectifieroutput current).

FIG. 2 shows illustrative wireless power circuitry in system 8 in anillustrative scenario in which a wireless power transmitting device hasbeen paired with a wireless power receiving device. The wireless powercircuitry of FIG. 2 includes wireless power transmitting circuitry 52 inwireless power transmitting device 12 and wireless power receivingcircuitry 54 in wireless power receiving device 24. During operation,wireless power signals 44 are transmitted by wireless power transmittingcircuitry 52 and are received by wireless power receiving circuitry 54.The configuration of FIG. 2 includes a single transmitting coil 36 and asingle receiving coil 48 (as an example).

As shown in FIG. 2 , wireless power transmitting circuitry 52 includesinverter circuitry 61. Inverter circuitry (inverter) 61 may be used toprovide signals to coil 36. During wireless power transmission, thecontrol circuitry of device 12 supplies signals to control input 82 ofinverter 61 that cause inverter 61 to supply alternating-current drivesignals to coil 36. Circuit components such as capacitor 70 may becoupled in series with coil 36 as shown in FIG. 2 . Measurementcircuitry 41 in device 12 may make measurements on operating currentsand voltages in device 12. For example, voltage sensor 41A may be usedto measure the coil voltage across coil 36 and current sensor 41B may beused to measure the coil current through coil 36. In otherimplementations, voltage across capacitor 70 is measured and currentthrough the coil is inferred from that measurement.

When alternating-current current signals are supplied to coil 36,corresponding alternating-current electromagnetic signals (wirelesspower signals 44) are transmitted to nearby coils such as illustrativecoil 48 in wireless power receiving circuitry 54. This induces acorresponding alternating-current (AC) current signal in coil 48.Capacitors such as capacitors 72 may be coupled in series with coil 48.Rectifier 50 receives the AC current from coil 48 and producescorresponding direct-current power (e.g., direct-current voltage Vrect)at output terminals 76. This power may be used to power a load.Measurement circuitry 43 in device 24 may make measurements on operatingcurrents and voltages in device 24. For example, voltage sensor 43A maymeasure Vrect (the output voltage of rectifier 50) or a voltage sensormay measure the coil voltage on coil 48. Current sensor 43B may measurethe rectifier output current of rectifier 50 or a current sensor maymeasure the current of coil 48.

If desired, some of the devices in wireless power system 8 may have boththe ability to transmit wireless power signals and to receive wirelesspower signals. A cellular telephone or other portable electronic devicemay, as an example, have a single coil that can be used to receivewireless power signals from a charging puck or other wireless powertransmitting device and that can also be used to transmit wireless powerto another wireless power device (e.g., another cellular telephone, anaccessory device, etc.). A device that can both transmit and receivewireless power may have all of the components of wireless powertransmitting device 12 and all the components of wireless powerreceiving device 24 (e.g., power transmitting circuitry 52 and powerreceiving circuitry 54 are included in a single device). However, thefunctionality of the wireless power transmission and the wireless powerreception is the same as described in connection with FIGS. 1 and 2 .Therefore, although the examples herein will focus on a scenario where adedicated wireless power transmitting device transfers charge to adedicated wireless power receiving device, it should be understood thata device that both transmits and receives wireless power may besubstituted for one or both devices.

FIG. 3 is a diagram of an illustrative power transmitting device withdithering circuitry. As previously mentioned, power transmitting device12 transmits AC signals to power receiving device 24 at a powertransmission frequency. The power transmission frequency may be between100-400 kHz or any other desired magnitude. A clock signal may beprovided to inverter circuitry 61 at the power transmission frequency tocause transistors in the inverter circuitry to turn on and off to createAC current signals through the wireless power transmitting coil (also atthe power transmission frequency).

Care may be taken to mitigate electromagnetic interference (EMI) insystem 8. One way to mitigate EMI in system 8 is to dither the clocksignal used to control inverter 61 in wireless power transmissioncircuitry 52. This effectively dithers the power transmission frequencyof the wireless power transfer between power transmitting device 12 andpower receiving device 24. As shown in FIG. 3 , power transmittingdevice 12 may include dithering circuitry 84 and clock modulatingcircuitry 86 that is used to perform frequency dithering during wirelesspower transfer operations. Dithering circuitry 84 and clock modulatingcircuitry 86 may be considered part of power transmission frequency 52and/or control circuitry 16 in device 12.

Dithering circuitry 84 may determine a modulating waveform 90 that isused to modulate the power transmission clock waveform 88. The clockwaveform 88 may have the same frequency as the power transmissionfrequency. To mitigate EMI in system 8, a modulating waveform 90 isapplied to clock waveform 88 by clock modulating circuitry 86. Clockmodulating circuitry 86 may use modulating waveform 90 to frequencymodulate clock waveform 88. The modified clock signal 92 is thenprovided to inverter 61 to create AC current signals for wireless powertransmission.

In one possible arrangement, dithering circuitry 84 and clock modulatingcircuitry 86 may be used to implement a spread spectrum clockingtechnique (sometimes referred to as clock dithering). In spread spectrumclocking, the edge of the clock waveform is intentionally modified suchthat the signal's spectrum is spread around the target frequency for theclock signal. This reduces the EMI associated with the target frequencyof the clock signal.

FIG. 4 is a graph of power as a function of frequency showing the effectof spread spectrum clocking. The graph of FIG. 4 may be obtained using aspectrum analyzer. Profile 94 shows the power as a function of frequencyfor a clock signal that does not undergo spread spectrum clocking (e.g.,a regular square wave or sinusoidal wave at a constant frequency). Asshown, without spread spectrum clocking, power peaks are present at eachharmonic of the power transmission frequency. FIG. 4 shows the N^(th)harmonic (e.g., the N^(th) multiple of the power transmissionfrequency), N+1 harmonic, and N+2 harmonic. At each harmonic, a narrowpeak is present. The height of the peaks may slowly decrease with anincreasing harmonic number.

Profile 96 shows the power as a function of frequency for a clock signalthat does undergo spread spectrum clocking. As shown, with spreadspectrum clocking, the power is lower at the harmonic frequenciescompared to the example without spread spectrum clocking (e.g., profile96 is lower than profile 94 at the N^(th) harmonic, N+1 harmonic, andN+2 harmonic). Between the harmonic frequencies, profile 96 is higherthan profile 94. Spread spectrum clocking essentially distributes thepower (and corresponding EMI) more evenly across the frequency spectrum(e.g., lowering power at the harmonic frequencies and increasing powerat the non-harmonic frequencies). Additional EMI is therefore present atthe non-harmonic frequencies relative to an unmodulated clock signal(e.g., profile 96 is higher than profile 94 between the harmonicfrequencies). However, the spread spectrum clocking may ultimately bebeneficial due to the reduced EMI at the harmonic frequencies.

FIG. 5 is a graph of an illustrative modulating waveform that may beused for spread spectrum clocking. The modulating waveform is used tofrequency modulate the carrier wave (e.g., the original clock waveform88). The modulating waveform may have a corresponding frequency f_(m)and a frequency spread Δf. Frequency f_(m) is the frequency ofmodulating wave 90. In other words, the modulating waveform sweepsbetween two fixed frequencies f₁ and f₂ at the frequency f_(m). Thedifference between frequencies f₁ and f₂ may sometimes be referred to asthe frequency spread or frequency deviation (Δf) of the modulatingwaveform.

For example consider the example where the wireless power system selectsa power transmission frequency of 140 kHz. The unmodified clock waveform88 may be a square wave or sinusoidal wave at 140 kHz. The modulatingwaveform 90 may have a frequency spread (Δf) of 10 kHz and a frequency(f_(m)) of 15 kHz. In this example, after waveform 88 is frequencymodulated with modulating waveform 90, the modified clock signal may, ata 15 kHz frequency, sweep back and forth between 135 kHz and 145 kHz. Inthis example, the frequency spread of the modulating waveform isdistributed evenly about the original frequency 140 kHz. This may bereferred to as a center spread. Alternatively, the frequency modulationmay be down spread (such that the modified clock signal sweeps back andforth between 130 kHz and 140 kHz) or up spread (such that the modifiedclock signal sweeps back and forth between 140 kHz and 150 kHz).

There are many options for the modulating waveform frequency f_(m),frequency deviation Δf, and waveform shape. Frequency f_(m) may begreater than 0 kHz, greater than 5 kHz, greater than 10 kHz, greaterthan 20 kHz, greater than 30 kHz, greater than 40 kHz, greater than 50kHz, greater than 75 kHz, greater than 100 kHz, greater than 200 kHz,less than 5 kHz, less than 10 kHz, less than 20 kHz, less than 30 kHz,less than 40 kHz, less than 50 kHz, less than 75 kHz, less than 100 kHz,less than 200 kHz, etc. Frequency deviation Δf may be greater than 0kHz, greater than 1 kHz, greater than 3 kHz, greater than 5 kHz greaterthan 10 kHz, greater than 20 kHz, greater than 30 kHz, greater than 40kHz, greater than 50 kHz, less than 1 kHz, less than 3 kHz, less than 5kHz less than 10 kHz, less than 20 kHz, less than 30 kHz, less than 40kHz, less than 50 kHz, etc. In FIG. 5 , modulating waveform 90 has atriangular shape. This example is merely illustrative. In general,modulating waveform 90 may have any desired shape (e.g., sinusoidalshape, square shape, sawtooth shape, a randomized shape, or a step shapethat approximates any of the aforementioned shapes).

FIGS. 6A and 6B are graphs of illustrative modulating waveforms 90 thatmay be used in clock signal dithering for wireless power transmission.FIG. 6A is an example of a waveform that has a step shape that follows aregular pattern (i.e., a regular step shape). In FIG. 6A, the regularstep shape approximates a sawtooth shape. The waveform increases insuccessive steps between a minimum frequency f₁ and a maximum frequencyf₂. Once f₂ is reached, the waveform returns to f₁ and repeats thepattern. In FIG. 6A, there are six frequencies used in the waveform(e.g., f₁, f₂, and four intervening frequencies). The duration the clocksignal spends at each frequency (e.g., the width of each step) may bethe same or approximately the same. Alternatively, the duration theclock signal spends at each frequency may be varied if desired.

In FIG. 6B, the modulating waveform 90 has an irregular step shape.Similar to as in FIG. 6A, the waveform of FIG. 6B may have successivesteps between a minimum frequency f₁ and a maximum frequency f₂. In FIG.6B, there are six frequencies used in the waveform (e.g., f₁, f₂, andfour intervening frequencies). However, in FIG. 6B, the frequencies arenot stepped through in ascending (or descending) order. The stepsproceed in a random order such that the waveform is not necessarilycontinuously increasing (as in FIG. 6A) or decreasing (e.g., an oppositearrangement to FIG. 6A). Using an irregular waveform of this type may beused to optimize the spread spectrum clocking in power transmissiondevice 12. The random order may be repeated in each cycle or may berandomized after each cycle.

A waveform with a stepped shape (in either a regular pattern as in FIG.6A or an irregular pattern as in FIG. 6B) may include any desired numberof steps (e.g., three, four, five, six, seven, eight, more than eight,more than ten, etc.).

To summarize, the modulating waveform may have a number of discretesteps. The sequence in which these frequency steps are taken and theduration of each frequency step may be optimized for EMI attenuation.The frequency steps may be sequenced in a periodic or random fashion.Optimal sequences may be found using exhaustive search techniques oroptimization techniques that use genetic algorithms and/or neuralnetworks.

FIG. 7 is a diagram of an illustrative system that may be used to testthe efficacy of various dithered clock signals. As shown, the systemincludes a host device 100. Host 100 may include computing equipmentsuch as a personal computer, laptop computer, tablet computer, orhandheld computing device. Host 100 may include one or more networkedcomputers. Host 100 may maintain a database of results, may be used insending commands to clock modulating circuitry 86, may be used insending commands to spectrum analyzer 102, may receive data fromspectrum analyzer 102, etc.

During operation of the system of FIG. 7 , host device 100 may send aplurality of different clock waveforms and modulating waveforms to clockmodulating circuitry 86. The clock modulating circuitry frequencymodulates the clock waveform using the modulating waveform and outputsthe corresponding modified clock signal to spectrum analyzer 102.Spectrum analyzer 102 measures the magnitude of the modified clocksignal across a range of frequencies to measure the power at differentfrequencies. Spectrum analyzer 102 may output data corresponding to agiven modified clock signal to host device 100. Host device 100 maymaintain a database of test results associated with different clockwaveforms and modulating waveforms.

FIG. 7 shows an example where spectrum analyzer 102 tests the modifiedclock signal provided directly from clock modulating circuitry 86. Thisexample is merely illustrative. If desired, the spectrum analyzer 102may instead test the alternating-current drive signals provided byinverter 61 to coil 36 based on the modified clock signal received byinverter 61. As yet another example, the spectrum analyzer 102 mayinstead test the alternating-current (AC) current signals that areinduced in coil 48. Circuit simulation tools may be used in addition toor instead of spectrum analyzer 102 to determine the performance of themodulated clock signals.

The operating parameters of spectrum analyzer 102 (e.g., centerfrequency, span, scan time, resolution bandwidth (RBW), video bandwidth(VBW), attenuation/amplification, etc.) may be tuned to obtain desiredspectrum data during testing operations.

Host device 100 may perform various tests to optimize the modulatingwaveform to have minimized EMI (maximum attenuation) at one or morefrequencies of interest during wireless power transfer operations. Forexample, power transmitting device 12 and/or power receiving device 24may have design constraints with EMI requirements at certainfrequencies. Host device 100 may optimize the modulating waveform tomeet all of these EMI requirements and reduce EMI as much as possible atthe frequencies of interest.

Host device 100 may test numerous frequency spreads (Δf) for themodulating waveform. For example, in one series of tests, the shape ofthe modulating waveform, properties of the clock waveform, modulatingwaveform frequency f_(m), and other operating conditions may remainconstant while different frequency spread magnitudes are used. The hostdevice may step through frequency spreads at regular intervals (e.g., x,2×, 3×, 4×, etc.) through a desired range of frequencies, may testvarious irregularly spaced frequency spreads, etc.

Small changes in Δf may have significant impacts on attenuation atcertain frequencies of interest. As an example, attenuation at a givenN^(th) harmonic may have improvements when the equation 2*Δf*N/f_(clock)(where Δf is the frequency spread, N is the harmonic number of interest,and f_(clock) is the frequency of the clock signal) is equal orapproximately equal to (e.g., within 5%, within 3%, within 1%, etc.) aneven integer. Take an example where f_(clock) is 360 kHz and attenuationis desired at the 85^(th) harmonic (30.6 MHz). Attenuation may havelocal maxima when Δf is equal to 8.5 kHz (where 2*Δf*N/f_(clock)≈4),12.7 kHz (where 2*Δf*N/f_(clock)≈6), and 16.9 kHz (where2*Δf*N/f_(clock)≈8). The learnings from the frequency spread tests maybe used to optimize frequency dithering of the clock signal insubsequent operations of a power transmitting device 12 (e.g., may beused to develop an algorithm used by dithering circuitry 84 in device 12to produce an optimal modulating waveform for real time conditions).

Host device 100 may also test numerous frequencies (f_(m)) for themodulating waveform. For example, in one series of tests, the shape ofthe modulating waveform, properties of the clock waveform, modulatingwaveform frequency spread Δf, and other operating conditions may remainconstant while different frequency magnitudes are used. The host devicemay step through frequencies at regular intervals (e.g., x, 2×, 3×, 4×,etc.) through a desired range of frequencies, may test variousirregularly spaced frequencies, etc. In one example, larger frequencies(e.g., 45 kHz) may have more attenuation at a wavelength of interest(e.g., the 85^(th) harmonic of 360 kHz) than lower frequencies (e.g., 5kHz, 10 kHz, 20 kHz). The learnings from the frequency tests may be usedto optimize frequency dithering of the clock signal in subsequentoperations of a power transmitting device 12 (e.g., may be used todevelop an algorithm used by dithering circuitry 84 in device 12 toproduce an optimal modulating waveform for real time conditions).

Host device 100 may also test numerous waveform shapes for themodulating waveform. For example, in one series of tests, the propertiesof the clock waveform, the frequency of the modulating waveform, thefrequency spread of the modulating waveform, and other operatingconditions may remain constant while different modulating waveformshapes are used (e.g., sawtooth, triangular, sine, square, etc.). Thehost device may test each shape to determine the magnitude ofattenuation at one or more wavelengths of interest for each shape. Inone example, a modulating waveform having a sawtooth shape may have moreattenuation at a wavelength of interest (e.g., the 85^(th) harmonic of360 kHz) than a modulating waveform having a triangular, sine, or squareshape. The learnings from the waveform shape tests may be used tooptimize frequency dithering of the clock signal in subsequentoperations of a power transmitting device 12 (e.g., may be used todevelop an algorithm used by dithering circuitry 84 in device 12 toproduce an optimal modulating waveform for real time conditions).

As previously mentioned, a modulating waveform may have a plurality offrequency steps (e.g., that approximate a sawtooth shape or otherdesired shape or that have a random order). For a modulating waveformhaving a plurality of frequency steps, the sequence in which thefrequency steps are taken and the duration of each frequency step may beoptimized. In one example, host device 100 may perform an exhaustivesearch on frequency-step-order given a number of constraints. As anexample, for a constant clock frequency, modulating waveform frequency,number of steps, and spread between each step, the order of thefrequency steps may be tested. Consider a 6-step profile approximating asawtooth shape (similar to as in FIG. 6A) that includes progressivelyincreasing frequencies f₁, f₂, f₃, f₄, f₅, and f₆ (e.g.,f₁<f₂<f₃<f₄<f₅<f₆). Host device may provide a modulating waveform withthese frequency steps in each possible permutation. For example, in afirst test, the waveform may have frequency steps in the order f₁, f₂,f₃, f₄, f₅, then f₆. In a second test, the waveform may have frequencysteps in the order f₁, f₂, f₃, f₄, f₆, then f₅. In a third test, thewaveform may have frequency steps in the order f₁, f₂, f₃, f₆, f₄, thenf₅. In a fourth test, the waveform may have frequency steps in the orderf₁, f₂, f₃, f₆, f₅, then f₄. This process may be repeated until eachpermutation of f₁-f₆ is tested (e.g., an exhaustive search). The bestcandidates (e.g., the sequences that produce the most attenuation at oneor more frequencies of interest) may be stored for future use inoptimizing frequency dithering of the clock signal in subsequentoperations of a power transmitting device 12 (e.g., may be used todevelop an algorithm used by dithering circuitry 84 in device 12 toproduce an optimal modulating waveform for real time conditions).

To summarize, any desired properties (e.g., frequency, frequency spread,waveform shape, frequency-step order, frequency-step duration, etc.) ofthe modulating waveform may be tested to determine the impact of thoseproperties on attenuation at frequencies of interest and find optimalvalues for those properties. The properties may be tested in isolation(as described above). However, this example is merely illustrative and,in general, combinations of properties may also be tested to findoptimal property sets.

Modulating waveforms may also be tested for efficacy under differentoperating conditions. During normal operating conditions (in the field),power transmission device 12 (with clock modulating circuitry 86)transmits power to power receiving device 24 while power receivingdevice 24 has different load conditions. The load current (e.g., thecurrent supplied by rectifier 50) of the power receiving device may varydepending on the operating state of the power receiving device (e.g.,which input-output components in the power receiving device are in use),the state of charge of the power receiving device, etc.

When operating under different load conditions, the waveform shape ofthe AC signals used for wireless power transfer may vary. For example,the duty cycle, rise time, fall time, undershoot, and/or overshoot ofthe AC signals (provided by inverter 61 and coil 36 and/or received bycoil 48) may vary depending on the load conditions of the wireless powerreceiving device. These changes in shape may influence the frequencydithering operations to mitigate EMI.

For example, power receiving device 24 may receive wireless power whilethe state of charge is equal to 20%. Under these conditions, the ACsignals may have a waveform shape that causes undesirably high EMI at afrequency f₁. A first dithering pattern (that optimizes EMI mitigationat f₁) may be optimal in these conditions. At a subsequent time, powerreceiving device 24 may receive wireless power while the state of chargeis equal to 80%. Under these conditions, the AC signals may have awaveform shape that causes undesirably high EMI at a frequency f₂ thatis different than f₁. A second dithering pattern (that optimizes EMImitigation at f₂) may be optimal in these conditions.

Additionally, given the different waveforms that result from thedifferent load conditions at different states of charge, mitigating EMIat a given frequency of interest may require different optimal ditheringpatterns at different states of charge. For example, power receivingdevice 24 may receive wireless power while the state of charge is equalto 20% and there is a corresponding first load current for the powerreceiving device. A first dithering pattern may be optimal to mitigateEMI at a frequency f₁ in these conditions. At a subsequent time, powerreceiving device 24 may receive wireless power while the state of chargeis equal to 80% and there is a corresponding second load current for thepower receiving device. A second dithering pattern that is differentthan the first dithering pattern may be optimal to mitigate EMI at thefrequency f₁ in these conditions.

For example, while the state-of-charge is equal to 20%, the optimalfrequency spread of the modulating waveform to mitigate EMI at f₁ may be10 kHz but while the state-of-charge is equal to 80%, the optimalfrequency spread of the modulating waveform to mitigate EMI at f₁ may be20 kHz. As another example, while the state-of-charge is equal to 20%,the optimal modulating waveform to mitigate EMI at f₁ may have asawtooth shape but while the state-of-charge is equal to 80%, theoptimal modulating waveform to mitigate EMI at f₁ may have a triangularshape. These examples are merely illustrative and demonstrate how themodulating waveform may have different optimal properties in differentoperating conditions.

To account for these differences, the aforementioned tests (e.g., usingthe system of FIG. 7 ) may also be performed at different operatingconditions. For example, tests may be performed while the powerreceiving device has different states of charge, different correspondingload conditions, etc.

Host device 100 may, in one possible embodiment, test the modulatingwaveform properties and only use direct test results for optimization ofthe modulating waveform. Alternatively, host device 100 may include amachine learning classifier that uses the test results to develop amachine learning algorithm that optimizes the modulating waveformproperties. The machine learning algorithm may output an optimizedmodulating waveform for a given set of constraints. The developedmachine learning algorithm may subsequently be used in ditheringcircuitry 84 in power transmitting device 12.

As described above, the state-of-charge of a wireless power receivingdevice may influence the optimal frequency dithering pattern forwireless power transmission. Therefore, it is desirable for wirelesspower transmitting device 12 to know the state of charge of wirelesspower receiving device 24 during wireless power transfer operations.When power transmitting device 12 knows the state of charge of wirelesspower receiving device 24, power transmitting device 12 can factor inthe state of charge when optimizing the frequency dithering pattern.

In some cases, the wireless power transmitting device 12 may receivestate of charge information directly from wireless power receivingdevice 24. The wireless power receiving device 24 may report its stateof charge to wireless power transmitting device 12 at regular intervals,when the state of charge changes by a certain amount from the previouslyreported state of charge, etc. Alternatively, wireless powertransmitting device 12 may intermittently query wireless power receivingdevice 24 for its state of charge. In response to receiving the query,wireless power receiving device 24 may report its state of charge towireless power transmitting device 12. These types of communications maybe performed either in-band (e.g., using coils 36 and 48 andsimultaneously with power transfer) or out-of-band (e.g., using separatecommunication antennas such as Bluetooth antennas).

When wireless power receiving device 24 reports its state of charge towireless power transmitting device 12, control circuitry within wirelesspower transmitting device 12 may decode data received from the wirelesspower receiving device. The decoded data may represent a state of chargemagnitude reported by the wireless power receiving device. The data maybe received by wireless power transmitting device 12 using the powertransmitting coil 36 (e.g., using in-band communication) or using anantenna formed separately from the coil (e.g., using out-of-bandcommunication).

Direct reporting of the state of charge is the most accurate way for thewireless power transmitting device 12 to determine the state of chargeof the wireless power receiving device 24. However, some wirelesscharging communication protocols may not involve (or allow) reporting ofstate of charge from the power receiving device to the powertransmitting device. In these instances, power transmitting device 12may measure parameters associated with power transfer coil 36 and usethese measured parameters to estimate the state of charge of receiver24.

As previously mentioned, measurement circuitry 41 in device 12 may makemeasurements on operating currents and voltages in device 12. Forexample, voltage sensor 41A may be used to measure the coil voltageacross coil 36 and current sensor 41B may be used to measure the coilcurrent through coil 36 (see FIG. 2 ). The coil voltage and coil currentmay be two parameters that wireless power transmitting device 12 uses toestimate the wireless power receiving device's state of charge.Additional parameters such as duty cycle (e.g., the duty cycle or theclock signal and corresponding AC drive signals generated by inverter61) may be used to estimate the wireless power receiving device's stateof charge. To summarize, control circuitry within power transmittingdevice 12 may determine an operating parameter of the wireless powertransmitting device 12 (e.g., coil voltage, coil current, etc.) in orderto determine wireless power receiving device state of chargeinformation.

While in certain embodiments it is beneficial for wireless transceiversto report information such as state of charge for feedback and powerdelivery control, the above-described technology need not involve thetransmission of personally identifiable information to function. Out ofan abundance of caution, it is noted that to the extent that anyimplementation of this charging technology involves the use of datacommunication between wireless power transmitters and receivers, theinformation communicated should be used for controlling power delivery,and implementers should follow privacy policies and practices that aregenerally recognized as meeting or exceeding industry or governmentalrequirements for maintaining the privacy of users.

FIG. 8 is a diagram of a system that may be used to determinecorrelations between power transmitting device parameters (such as dutycycle, coil voltage, and/or coil current) and the state of charge ofpower receiving device 24. As shown in FIG. 8 , a host device 100 may beconnected to a wireless power transmitting device 12 and a wirelesspower receiving device 24. Host 100 may include computing equipment suchas a personal computer, laptop computer, tablet computer, or handheldcomputing device. Host 100 may include one or more networked computers.Host 100 may maintain a database of results, may be used in sendingcommands to wireless power transmitting device 12 and/or wireless powerreceiving device 24, may receive data from wireless power transmittingdevice 12 and/or wireless power receiving device 24, etc.

Host 100 may obtain data on the wireless power transmitting device 12while wireless power receiving device 24 is at various known states ofcharge. For example, wireless power transmitting device parameters(e.g., duty cycle, coil current, and coil voltage) may be measuredduring power transfer while wireless power receiving device 24 has afirst state of charge (e.g., 25%), wireless power transmitting deviceparameters (e.g., duty cycle, coil current, and coil voltage) may bemeasured during power transfer while wireless power receiving device 24has a second state of charge that is different than the first state ofcharge (e.g., 50%), wireless power transmitting device parameters (e.g.,duty cycle, coil current, and coil voltage) may be measured during powertransfer while wireless power receiving device 24 has a third state ofcharge that is different than the second state of charge (e.g., 75%),etc. A machine learning classifier may use the test results to develop amachine learning algorithm that estimates receiver state of charge basedon transmitter operating parameters. The developed machine learningalgorithm may subsequently be used in dithering circuitry 84 in powertransmitting device 12.

Therefore, instead of or in addition to using direct-reported state ofcharge information, wireless power transmitting device 12 may use proxyinformation (e.g., transmitter duty cycle, transmitter coil current,transmitter coil voltage) to estimate the receiver's state of charge.For simplicity, both direct-reported receiver state of chargeinformation and proxy information for receiver state of charge may bereferred to herein as state of charge information (or receiver state ofcharge information). Said another way, power transmitting device 12 maydetermine the receiver state of charge information using decoded datareceived directly from the power receiving device 24 (e.g.,direct-reported data) or using operating parameters of the powertransmitting device (e.g., proxy information).

The testing operations described in connection with FIGS. 7 and 8 may beused to develop an optimization algorithm that is used by ditheringcircuitry 84 to determine an optimal modulating waveform for a given setof conditions and constraints.

FIG. 9 is a diagram of dithering circuitry 84 showing the various inputsused by the dithering circuity to determine an optimized modulatingwaveform. As shown in FIG. 9 , dithering circuitry 84 may receivereceiver state of charge information. As previously discussed, thereceiver state of charge information may include either direct-reportedreceiver state of charge information (e.g., a state of charge reportedby the power receiving device to the power transmitting device usingin-band or out-of-band communication) or proxy information for receiverstate of charge (e.g., the duty cycle, current, or voltage for thetransmitting coil 36 in device 12). The proxy information may includemeasured/known transmitting device parameters as well as known (e.g.,through in-band or out-of-band communication) receiving deviceparameters. When dithering circuitry 84 receives proxy information forthe receiver state of charge, dithering circuitry 84 may estimate thereceiver state of charge using the proxy information and use theestimated state of charge for subsequent determinations.

In addition to receiver state of charge information, dithering circuitry84 may receive constraints such as a maximum frequency jitterconstraint. The maximum frequency jitter constraint may be fixed or maybe updated over time (e.g., by control circuitry 16).

An occupied bandwidth constraint may also be taken into account bydithering circuitry 84. Occupied bandwidth refers to the range offrequencies that contain the majority of the modulated communicationsignal power. Various communication standards have limits on theoccupied bandwidth's range. These occupied bandwidth constraints maylimit, for example, the magnitude of frequency spread Δf for themodulating waveform output by dithering circuitry 84.

Dithering circuitry 84 may also receive information on the wirelesspower receiving device 24 (RX parameters) and wireless powertransmitting device 12 (TX parameters). The receiver parameters receivedby dithering circuitry 84 may include the output voltage of rectifier 50(as measured by voltage sensor 43A), a voltage of coil 48 in the powerreceiving device, a rectifier output current of rectifier 50 (asmeasured by current sensor 43B in FIG. 2 ), or a current of coil 48 inthe power receiving device. This information may be received at wirelesspower transmitting device 12 from wireless power receiving device 24using in-band communication or out-of-band communication. In some cases,device 12 may also or instead have a priori knowledge of certainoperating parameters of device 24 (e.g., device type, coilcharacteristics, etc.) that are used by dithering circuitry 84 todetermine an optimized modulating waveform.

The wireless power transmitting device parameters may include thevoltage of coil 36 (as measured by voltage sensor 41A), the current ofcoil 36 (as measured by current sensor 41B), the duty cycle of inverter61, etc.

Dithering circuitry 84 may also receive information regarding the clockwaveform (e.g., the target for the dithering operations). In somewireless charging systems, the power transmission frequency may benegotiated between devices 12 and 24 (e.g., the power transmissionfrequency is not fixed). As an example, power transmitting device 12 maytransmit wireless power signals at a frequency of 120 kHz when a firstwireless power receiving device is adjacent to the power transmittingdevice. Subsequently, transmitting device 12 may transmit wireless powersignals at a frequency of 180 kHz when a second wireless power receivingdevice is adjacent to the power transmitting device (or when the firstwireless power receiving device is removed and again placed adjacent tothe power transmitting device). Accordingly, the frequency (and shape)of the clock signal for a given power transmission session may beprovided to dithering circuitry 84.

Dithering circuitry 84 may also have a dithering sequence memoryconstraint, as shown in FIG. 9 . The memory constraint may, as anexample, result in limits on the number of frequency steps permitted ina stepped waveform shape.

Based on all of these inputs, the dithering circuitry 84 outputs anoptimized modulating waveform. The optimized modulating waveform issubsequently used by clock modulating circuitry 86 to dither the clockwaveform. The modified (dithered) clock signal is then provided toinverter 61 to apply AC drive signals to coil 36 and transmit wirelesspower to coil 48 in wireless power receiving device 24. In other words,the power transmission frequency is dithered based on the optimizedmodulating waveform.

It should be understood that dithering circuitry 84 may provide theproperties of the modulating waveform to clock modulating circuitry ifdesired. For example, dithering circuitry 84 provides clock modulatingcircuitry with a frequency, frequency spread, and waveform shape for themodulating waveform. Clock modulating circuitry 86 then uses thereceived properties characterizing the modulating waveform to modulatethe clock waveform.

FIG. 10 is a flow chart of illustrative operations involved in using awireless power system in accordance with an embodiment. As shown, atstep 202, dithering circuitry such as dithering circuitry 84 (which maybe considered part of control circuitry 16 and/or power transmissioncircuitry 52) may gather information. The gathered information mayinclude any of the inputs shown in FIG. 9 including wireless powerreceiving device state of charge information, a maximum frequency jitterconstraint, an occupied bandwidth constraint, wireless power receivingdevice parameters, wireless power transmitting device parameters, and aclock waveform. The received information may be received from sensorswithin power transmitting device 12 (e.g., voltage sensor 41A or currentsensor 41B in FIG. 2 ), may be received from device 24 (e.g., usingin-band communication or using out-of-band communication), may bereceived from control circuitry 16, may be derived based on knowninformation within the transmitting device, etc.

At step 204, control circuitry within power transmitting device 12(e.g., dithering circuitry 84) may use the gathered information todetermine an optimal modulating waveform for the current operatingconditions. The optimal modulating waveform may have a correspondingfrequency, frequency spread, shape, etc. Dithering circuitry 84 may usean algorithm to determine the optimal modulating waveform. The algorithmmay be developed using machine learning techniques (e.g., neuralnetworks, genetic algorithms, etc.) if desired. In some cases, theoptimal waveform shape may be a randomized shape (e.g., with arandomized sequence of frequency steps as discussed in connection withFIGS. 6A and 6B). The optimized dithering pattern may conform to anyconstraints received by the dithering circuitry (e.g., occupiedbandwidth constraint, dithering sequence memory constraint, maximumfrequency jitter constraint, etc.).

As one example, dithering circuitry 84 may calculate an optimalmodulated waveform depending on the current operating conditions. Asanother example, dithering circuitry 84 may have a plurality ofmodulating waveforms stored in memory. Each one of the modulatingwaveforms may have an associated set of operating conditions. Ditheringcircuitry 84 may select a modulating waveform from memory withassociated operating conditions that best matches the real-timeoperating conditions and also that meets any real-time constraints.

Finally, at step 206, the optimized dithering pattern (e.g., the optimalmodulating waveform) may be used to modulate the clock waveform (e.g.,as shown in FIG. 3 ). The modified (dithered) clock signal is providedto inverter 61 to generate AC signals with coil 36.

As previously mentioned, frequency-shift keying (FSK) may be used toconvey in-band data from device 12 to device 24. Power may be conveyedwirelessly from device 12 to device 24 during these FSK transmissions.Frequency dithering (as described above) may also be performed duringFSK transmissions.

During FSK modulation, power transmitting device 12 may switch itsoperating frequency between a first operating frequency (e.g.,unmodulated operating frequency f_(op)) and a second operating frequency(e.g., modulated operating frequency f_(mod)). The difference betweenthe two frequencies has both a polarity (indicating whether thedifference between f_(mod) and f_(op) is positive or negative) and adepth (indicating the magnitude of the difference between f_(mod) andf_(op)).

Using the unmodulated operating frequency and the selected modulatedoperating frequency, the power transmitter may transmit bits using FSKmodulation. The power transmitter may use a bit encoding scheme totransmit the bits using FSK modulation. In one illustrative example, thepower transmitter may use a differential bi-phase encoding scheme tomodulate data bits using the power signal. This type of bi-phaseencoding scheme is shown in FIG. 11 .

FIG. 11 shows the power signal frequency over time during FSKmodulation. The power signal frequency transitions between frequenciesf₁ and f₂ to encode bits. Frequencies f₁ and f₂ may be equal to f_(op)and f_(mod) as discussed previously, with either f_(op) or f_(mod) beingthe higher of the two frequencies. As shown, in the encoding scheme ofFIG. 11 , a transition between the two frequencies occurs at the startof each bit. To encode a ‘one’ bit, there are two transitions in thepower signal frequency. To encode a ‘zero’ bit, there is one transitionin the power signal frequency.

For example, at t₁ the operating frequency (power signal frequency)transitions from f₂ to f₁. This indicates the start of encoding the onebit. The operating frequency may remain at f₁ for a given number ofcycles of the power signal (e.g., 256 cycles) then transition back to f₂at t₂. The operating frequency remains at f₂ for the given number ofcycles. At t₃, the encoding of the one bit is complete.

At t₃, the operating frequency (power signal frequency) transitions fromf₂ to f₁. This indicates the start of encoding the zero bit. Theoperating frequency may remain at f₁ for a given number of cycles (e.g.,512 cycles) then transition back to f₂ at t₄. At t₄, the encoding of thezero bit is complete.

To summarize, each bit (either a ‘one’ or ‘zero’) is transmitted overthe same period of time (e.g., duration T₂ in FIG. 11 ). This period oftime may sometimes be referred to as a bit period. For a zero bit, theoperating frequency transitions once at the beginning of the bit periodand then remains at the same operating frequency for the entire bitperiod (T₂). For a one bit, the operating frequency transitions once atthe beginning of the bit period and again halfway through transmissionof the bit. During encoding of a one bit, the operating frequency istherefore at both frequencies f₁ and f₂ for an equal duration of time T₁that is half of T₂.

During encoding of bits using the differential bi-phase encoding schemeof FIG. 11 , the frequency remains constant for either a duration oftime T₂ or T₁ before transitioning to the other frequency. T₁ is half ofT₂. These periods of time where the frequency is constant may bereferred to as modulation states. The modulation states are used toconvey bits using the bit encoding scheme.

To prevent the frequency dithering from impacting FSK communications,the dither pattern may repeat after a number of cycles of the powersignal that is equal to a sub-multiple of (e.g., an exact divisor of)the number of power cycles in T₁ in FIG. 11 (e.g., the length of theshortest modulation state in the encoding scheme). For example, considerthe example above where T₁ is equal to 256 cycles of the power signal.In this case, the total length of the repeating dither pattern (e.g.,the period of the modulating waveform in FIGS. 3, 5, 6A, or 6B) may beequal to any sub-multiple of 256 cycles (e.g., 1 cycle, 2 cycles, 4cycles, 8 cycles, 16 cycles, 32 cycles, 64 cycles, 128 cycles, or 256cycles). This ensures that the dither pattern is completed within agiven modulation state and does not traverse multiple modulation states,which may simplify FSK demodulation for the receiver of the FSKcommunications (e.g., power receiving device 24).

This concept of selecting the total length of the repeating ditherpattern to be equal to a sub-multiple of the total length of theshortest modulation state in the FSK encoding scheme may be used bothfor FSK communications from a wireless power transmitting device to awireless power receiving device or for FSK communications from awireless power receiving device to a wireless power transmitting device.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A wireless power transmitting device configuredto provide wireless power to a wireless power receiving device,comprising: wireless power transmitting circuitry having an inverter anda wireless power transmitting coil, wherein the inverter is configuredto receive a clock signal and supply corresponding alternating-currentdrive signals to the wireless power transmitting coil; and controlcircuitry configured to, based at least partly on wireless powerreceiving device state of charge information, frequency dither the clocksignal provided to the inverter.
 2. The wireless power transmittingdevice of claim 1, wherein frequency dithering the clock signalcomprises: determining a modulating waveform based at least partly onthe wireless power receiving device state of charge information; andmodulating the clock signal using the modulating waveform.
 3. Thewireless power transmitting device of claim 2, wherein determining themodulating waveform comprises determining a frequency, a frequencyspread, and a shape for the modulating waveform.
 4. The wireless powertransmitting device of claim 1, wherein the control circuitry is furtherconfigured to determine the wireless power receiving device state ofcharge information by determining an operating parameter of the wirelesspower transmitting device.
 5. The wireless power transmitting device ofclaim 4, wherein determining the operating parameter comprisesdetermining a voltage or current measurement of the wireless powertransmitting coil.
 6. The wireless power transmitting device of claim 1,wherein the control circuitry is further configured to determine thewireless power receiving device state of charge information by decodingdata received from the wireless power receiving device, wherein thedecoded data represents a state of charge magnitude reported by thewireless power receiving device.
 7. The wireless power transmittingdevice of claim 6, wherein the control circuitry receives the data fromthe wireless power receiving device using the wireless powertransmitting coil.
 8. The wireless power transmitting device of claim 6,further comprising: an antenna formed separately from the wireless powertransmitting coil, wherein the control circuitry receives the data fromthe wireless power receiving device using the antenna.
 9. The wirelesspower transmitting device of claim 1, wherein the control circuitry isconfigured to frequency dither the clock signal based at least partly onan occupied bandwidth constraint.
 10. The wireless power transmittingdevice of claim 1, wherein the control circuitry is configured tofrequency dither the clock signal based at least partly on a maximumfrequency jitter constraint.
 11. The wireless power transmitting deviceof claim 1, wherein the control circuitry is configured to frequencydither the clock signal based at least partly on a target powertransmission frequency for the alternating-current drive signals.
 12. Anon-transitory computer-readable storage medium storing one or moreprograms configured to be executed by one or more processors of awireless power transmitting device that is configured to providewireless power to a wireless power receiving device, wherein thewireless power transmitting device comprises wireless power transmittingcircuitry having an inverter and a wireless power transmitting coil andwherein the inverter is configured to receive a clock signal and supplycorresponding alternating-current drive signals to the wireless powertransmitting coil, the one or more programs including instructions for:based at least partly on wireless power receiving device state of chargeinformation, frequency dithering the clock signal provided to theinverter.
 13. The non-transitory computer-readable storage medium ofclaim 12, wherein frequency dithering the clock signal comprises:determining a modulating waveform based at least partly on the wirelesspower receiving device state of charge information; and modulating theclock signal using the modulating waveform.
 14. The non-transitorycomputer-readable storage medium of claim 13, wherein determining themodulating waveform comprises determining a frequency, a frequencyspread, and a shape for the modulating waveform.
 15. The non-transitorycomputer-readable storage medium of claim 12, wherein frequencydithering the clock signal comprises frequency dithering the clocksignal based at least partly on an occupied bandwidth constraint. 16.The non-transitory computer-readable storage medium of claim 12, whereinfrequency dithering the clock signal comprises frequency dithering theclock signal based at least partly on a maximum frequency jitterconstraint.
 17. The non-transitory computer-readable storage medium ofclaim 12, wherein frequency dithering the clock signal comprisesfrequency dithering the clock signal based at least partly on a targetpower transmission frequency for the alternating-current drive signals.18. The non-transitory computer-readable storage medium of claim 12,wherein the one or more programs further include instructions for:determining the wireless power receiving device state of chargeinformation by determining an operating parameter of the wireless powertransmitting device.
 19. A method of operating a wireless powertransmitting device that is configured to provide wireless power to awireless power receiving device, wherein the wireless power transmittingdevice comprises wireless power transmitting circuitry having aninverter and a wireless power transmitting coil and wherein the inverteris configured to receive a clock signal and supply correspondingalternating-current drive signals to the wireless power transmittingcoil, the method comprising: based at least partly on wireless powerreceiving device state of charge information, frequency dithering theclock signal provided to the inverter.
 20. The method of claim 19,wherein frequency dithering the clock signal comprises: determining amodulating waveform based at least partly on the wireless powerreceiving device state of charge information; and modulating the clocksignal using the modulating waveform.